JPS6233734A - Zirconium alloy having high corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain a Zr alloy having high corrosion resistance by blending Zr with specified amounts of Sn, Fe, Cr and Mo. CONSTITUTION:The composition of an alloy is composed of, by weight, 1-2% Sn, 0.1-0.3% Fe, 0.05-0.2% Cr, 0.05-5% Mo and the balance Zr. The alloy is subjected to cold plastic working and annealing to precipitate an intermetallic compound of the added elements in the Zr alloy. The composition may further contain one or more among 0.03-0.1% Ni, 0.05-5% Nb and 0.05-5% V.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a novel highly corrosion-resistant zirconium-based alloy,
In particular, the present invention relates to a BWR fuel assembly member having excellent nodular corrosion resistance.

[Background of the invention]

Zirconium-based alloys are used in structural members of atomic couplant fuel assemblies due to their excellent corrosion resistance and very small thermal neutron absorption cross sections.

Since these members are used in a furnace for a long time, their corrosion resistance is especially important. A typical example of a zirconium-based alloy is "Zircaloy-2" (Zr containing about 1.0% Sn).
5%, Fe approximately 0.1%.

Alloy containing approximately 0.1% Cr and approximately 0.05% Ni)
and “Zircaloy-4J (approximately 1.5% Sn in Zr)
, an alloy containing approximately 0.2% Fe and approximately 0.1% Cr)
It has been known. Also, Scatarch alloy (2, 3, 4, 5
, 6 with 0.4 to 1.2% Nb in zirconium.
, Sn 0.09% or less.

0.04% Fe and 0.01 to 0.5% Cr. M.

It has been reported that an alloy containing approximately 0.3% of

Zircaloy-2 and Zircaloy-2 mentioned above are fully performing their functions under the current operating conditions of nuclear reactors, but in the future, from the viewpoint of improving the economic efficiency of nuclear couplants, the operating period will be extended, and even harsher operating conditions will be required. is expected to be added. Therefore, a zirconium-based alloy with better corrosion resistance than the current state is desired.

In structural members of zirconium-based alloy BWR fuel assemblies, speckled grayish-white corrosion products called nodular corrosion are generated on the surface. When used for a long time in a nuclear reactor, if these corrosion products grow large enough, there is a risk that they will peel off. There is a concern that the decrease in the wall thickness of the member due to this peeling will result in a decrease in the mechanical strength of the fuel structural member.

FIG. 3 is a schematic diagram of a BWR fuel assembly. First, a spacer 4 that holds a large number of fuel rods (roughly divided into fuel pellets 1, fuel cladding tubes 2 and end plugs 3 covering the fuel pellets) at a predetermined distance from each other, It consists of a rectangular channel box 5 extending along the longitudinal direction of the fuel rods on the outside, and these play an important role in terms of fuel efficiency and plant safety.

Channel boxes are manufactured by forming plates into rectangular tubes and butt welding their joints. The spacer is similarly assembled by welding.

As shown in Figure 5, the fuel cladding tube is in contact with the fuel pellets on the inside and with the reactor water on the outside, and is a strength member, as well as corrosion resistant from corrosive gases (such as iodine) generated during combustion and the reactor water. used in the environment. It is particularly important to prevent nodular corrosion on the outer surface that comes into contact with reactor water.

The fuel spacer fixes a large number of fuel rods at several positions along the length of the fuel assembly, and prevents the fuel rods from vibrating in the lateral direction or bending in the longitudinal direction. 6 shows a plan view of the spacer, and FIG. 7 shows a side view of the spacer, in which the cladding tube 2 is fixed by a spacer grid 6 and a lantern-type leaf spring 7. For this reason, the spacer is used under stress from the fuel rods. Since this member comes into contact with reactor water, there is a risk of nodular corrosion.

The fuel channel box is located outside the fuel rods assembled with the fuel spacer, and is used with the fuel rods fixed by the upper tie plate 8 and the lower tie plate 9. Figure 8 shows an enlarged view of the fuel channel box.
The rectangular tube-shaped member is made by welding two divided plates into a rectangular tube shape that forcibly guides high-temperature water and steam generated in the fuel rods during operation to the top, and the rectangular tube is loaded with stress that spreads outward. used for long periods of time. Since this member also comes into contact with reactor water, it must have excellent nodular corrosion resistance.

Furthermore, for parts, hydrogen is generated during the oxidation reaction of zirconium-based alloys (Z r + 2 HzO- + Z r○
2+21'z), and there is a concern that this hydrogen accumulates in the material, impairing the strength of the material and having an adverse effect on the nodular corrosion resistance.

For this reason, materials with excellent nodular corrosion resistance will be increasingly required for materials for fuel cladding tube fuel spacers and construction channel boxes.

For this reason, materials with better corrosion resistance are being considered in place of Zircaloy alloys. Among these, Zr of Zr-Nb alloy
-2.5% Nb alloy is used in pressure pipes in a Canadian plant. The mechanical properties of this material are Zr-2,5~4.0%Sn-0,5~ which is said to have been modified by irradiation growth.
1, 5% Mo-0, 5-1.5% Nb alloy (Japanese Unexamined Patent Publication No. 51-134304).

In addition, Scatarch alloy (Zr-0.25~1.5%Nb-0) is said to have better corrosion resistance than Zircaloy.
,025~0.2%5n-0,02~1.0%(Cr+
Mo), or Zr-0,45-1.2%Nb-0,04
~0.1%5n-0,25~0.6% (Cr+Mo)
-0.7~0.7~1.8% (Nb+Cr+M
o) (Japanese Unexamined Patent Publication No. 5O-148213), and Zircaloy-4 with 0.5% and 1.0% Nb added (Nucl, 5cie, and E
ng Danyu (1977)).

However, with the exception of Zr-2,5%Nb alloy, most of these materials have no experience in use, and are said to be insufficient to replace Zircaloy alloys.

[Purpose of the invention]

An object of the present invention is to provide a zirconium alloy with excellent nodular corrosion resistance.

[Summary of the invention]

The present invention consists of 1-2% tin, 0.1-0.3% iron, 0.05-0.2% chromium, and 5% molybdenum by weight.
0%, the remainder consists of zirconium, or N
i O, 03-0.1%, NbO, 05-5% and Vo
, 05 to 5%.

The present inventors investigated ways to improve nodular corrosion resistance without significantly changing the chemical composition of Zircaloy.
I discovered the following facts.

That is, an ingot containing a small amount of MO added to a Zircaloy alloy was processed into a plate material through the steps of forging, hot plastic working, cold plastic working, and annealing, and then a corrosion test was conducted.

As a result, it was found that addition of Mo significantly improved nodular corrosion resistance.

This effect becomes more pronounced when a combination of Nb and V is added in addition to Mo. It has been found that this method is easier to manufacture and significantly improves the corrosion resistance compared to the method of hardening Zircaloy from the temperature of the β or β+α phase, which is known as the conventional heat treatment for improving corrosion resistance of Zircaloy.

Next, the range of the chemical components of the present inventor is shown.

Sn has the effect of suppressing the negative effect of reducing corrosion resistance due to nitrogen in zirconium-based alloys, so it is recommended to add 1 to 2%. If it is less than 1%, the effect will be small, and if it is added more than 2%, there will be no problem with corrosion resistance. is not good for mechanical properties.

The addition of Fe and Ni is effective in improving the corrosion resistance and mechanical properties of zirconium-based alloys. Therefore, each element is 0.
The content is preferably in the range of 0.05 to 0.3%. 0.
If the amount is less than 0.05%, the effect will be small, and if it is added more than 0.3%, it will have an adverse effect on the core properties and the ductility of the member.

Addition of a small amount of MO is effective in improving nodule corrosion resistance. In addition to the addition of MO, the combined addition of trace amounts of Nb and V provides stable corrosion resistance with a smaller addition amount. In addition, the amount of elements added is preferably 0.05 to 5.0% for Mo alone, and Nb and V (7) or two.
It is more effective to add seeds in an amount of 0.05 to 5.0%.

The reason for setting the upper limit for the amount of addition of these elements is that intermetallic compounds or metal second phases precipitate in large quantities due to the metallographic structure, and the elements that contribute to corrosion resistance become saturated in the matrix of the alloy. These are effective in nodular corrosion resistance. On the other hand, these precipitations are basically undesirable because they reduce the workability and ductility of the member, and at the same time, their addition in large amounts is undesirable in terms of nuclear properties.In other words, the thermal neutron absorption cross section of these elements is significantly larger than that of Zr. This is because the neutron economy decreases. In particular, the amount of Mo added is preferably 0.2 to 1.0% by weight, and 0.2 to 0.0% by weight.
5% is particularly preferred. In addition, the amount of Nb and ■ added is 0.0
5-1.0% is preferable, and 0.1-0.3% is more preferable.

The remainder consists of zirconium, unavoidable impurities, and oxygen, which has a large effect on strength.

Within the chemical composition range of the present invention, there is no significant change in plastic workability or weldability compared to conventional materials, and in terms of corrosion resistance, the fuel cladding tube is manufactured using a normal manufacturing process.

It has been found that the nodular corrosion resistance of fuel spacers and fuel channel boxes can be significantly improved.

The zirconium-based alloy of the present invention exhibits particularly remarkable effects when it is processed by repeating cold working and annealing at least three times after hot working. In both hot working and annealing after cold working, intermetallic compounds due to added elements in the zirconium alloy precipitate, and the excessive precipitation reduces corrosion resistance. However, the alloy of the present invention has remarkable corrosion resistance because the precipitation is suppressed.

Hot working temperature is 650-750℃ and annealing temperature is 550℃
Preferably, the temperature is 700°C. especially.

The final annealing is preferably performed at 500-550°C.

Furthermore, the zirconium-based alloy of the present invention has a remarkable effect particularly on butt welds. As mentioned above, the welding heat affected zone is formed with debris and its corrosion resistance is reduced, so this method is effective in such cases.

[Embodiments of the invention]

Example 1 Industrial cotton Zr was coated with about 0.15% Sn, 0.15% by weight. +
A master alloy containing 6% Fe, 0.1.0% Cr, and 0.05% N1 was melted, and approximately 0.3% MO was further added to the master alloy.

Sita alloys containing 0.5%, i, 0%, 5.0%, and 10% were melted. Each sample was solution treated at 1000°C, then hot rolled at 750'C and cold rolled at 600°C.
The annealing process was repeated three times and processed into a thin plate. The cold working rate was 70% in area reduction rate.

A corrosion test piece was taken from the thin plate and subjected to a corrosion test in high temperature steam. Test conditions were 510℃ and 105kg/at! It was kept in superheated steam for 20 hours. After the test, the weight of the test piece was measured and the appearance was inspected.

FIG. 1 is a diagram showing the relationship between corrosion weight gain and MO content. From the figure, it was found that addition of MO significantly reduced corrosion weight gain. In particular, the effect appears with a trace amount of content,
As a result of observing the appearance of the test piece after the corrosion test where the effect is saturated at about 0.5%, the test piece that does not contain Mo shows white nodular corrosion, but the test piece with 0.5% MO added is black. It exhibited a uniform oxide film.

Note that those containing 0.5% or more of 1Mo also had a similar appearance. It has thus been found that the nodular corrosion resistance of Zr-based alloys is significantly improved by containing MO.

On the other hand, a tensile test piece was taken from the above-mentioned thin plate and tested at room temperature. The elongation results are shown in FIG.

The elongation of the test piece to which Mo is added is equivalent to the value of the test piece to which Mo is not added, but when it exceeds 5%, the elongation rate gradually decreases. Therefore, in terms of ductility, the amount of Mo added should be 5% or less.

Example 2 Master alloy used in Example 1 (0.15% Sn.

An alloy was prepared by adding approximately 0.1% MO and 0.5% ■ to 0.16% Fe, 0.10% Cr, 0.05% Ni). The sample was hot worked at 750°C, followed by cold working and annealed at 600°C, and processed into a 1.5 nut plate.

Corrosion test pieces were taken from thin plates and tested at 510℃ and 105kg/
Corrosion resistance was evaluated by holding in ffl steam for 20 hours.

The corrosion weight increase of the material of the present invention is 50 mg/dm2, which is significantly lower than the 1050 mg/dm2 of the conventional material, and the appearance of the test piece shows a black uniform oxide film, making it resistant to nodular corrosion. It turns out that she has excellent sex.

Example 3 Industrial cotton Zr was used as the material, predetermined alloying elements were added, and an ingot was made by arc melting. Table 1 shows its chemical composition. Each ingot was processed into a pipe material by carrying out the material manufacturing process shown in Fig. In addition, the samples were divided into two types of hot working temperatures during the manufacturing process so that it was possible to confirm the presence or absence of the influence of the working temperature.

To evaluate the corrosion resistance, a long pipe material was cut into a length of about 50an to take a corrosion test piece, and then it was heated at 530°C and 105°C.
A corrosion test was conducted for 20 hours in kg/- steam. The test results are shown in Table 2. The corrosion characteristics of the comparison materials are as follows: The corrosion increase is 450 mg/dm for the Nα1 A-processed material, and 100 mg/dm for the 3-processed material.
0m g/dm” or more, and the specimen appearance a
Nodular corrosion is observed in a significantly large amount in m. Note that the characteristic of processed material A is that the corrosion weight gain is lower than that of processed material B, but when viewed in terms of nodular corrosion susceptibility, there is not much difference.

Table 2 In contrast, the corrosion weight increase of all samples of the present invention material was at a low level of 50 to 60 mg/dm'' regardless of the processing method, and the external observation results of the test pieces also showed black uniform oxidation and nodularity. No corrosion is observed.

As described above, the fuel cladding tube manufactured with the chemical composition of the present invention exhibits superior nodular corrosion resistance compared to conventional materials.

[Example 4] Regarding the evaluation of product plates, a portion was cut out from the ingot produced in Example 3 and processed into plates in the fuel spacer manufacturing process and the fuel channel box manufacturing process shown in FIG. 4, respectively. For the corrosion test, corrosion test pieces with a width of 30 nm, a length of 50 m, and thickness as they were were taken from these plates, and the corrosion conditions used in Example 3 were used. As a result, nodular corrosion occurred significantly in the comparative material, whereas nodular corrosion was not observed in the inventive material at all.As seen above, the corrosion resistance of fuel spacers and channel boxes was dramatically improved by using the inventive material. I found that it improved.

〔Effect of the invention〕

According to the present invention, a zirconium alloy with extremely low nodular corrosion resistance can be obtained, so it is expected that highly reliable fuel cladding tubes, fuel spacers, and fuel channel boxes using the same can be obtained.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between corrosion weight increase and Mo addition amount, Figure 2 is a diagram showing the relationship between elongation and Mo addition amount, Figure 3 is a cross-sectional view of the fuel assembly, and Figure 4 is the fuel Figure 5 is an exploded view of the fuel rod, Figure 6 is a plan view of the fuel spacer, Figure 7 is a side view of the fuel spacer, Figure 8 is a perspective view of the fuel channel box, FIG. 9 is a diagram of the manufacturing process of the tube material. 1...Fuel pellets, 2...Fuel cladding tube, 3...
End plug, 4...Fuel spacer, 5...Fuel channel box, 6...Spacer brit, 7...Lantern type leaf spring, 8...Upper tie plate, 9...Lower tie plate 1 ,'□ m, wood 01t (-'10) Invitation 2 figure f"lo ring tocal quantity (wtγ.) 纂(+ figure

Claims (1)

[Claims] 1. By weight: 1-2% tin, 0.1-0.3% iron, 0.05-0.2% chromium, and 0.05-5.0% molybdenum.
A highly corrosion-resistant zirconium-based alloy characterized by containing zirconium and the remainder zirconium. 2. The highly corrosion-resistant zirconium-based alloy according to claim 1, wherein the alloy is subjected to cold plastic working and annealing after the working, and has a prayer object. 3. The highly corrosion-resistant zirconium-based alloy according to claim 1 or 2, wherein the alloy is welded and joined and has a desired shape. 4. By weight, tin 1-2%, iron 0.1-0.3%, chromium 0.05-0.2% and molybdenum 0.05-5.0%
, nickel 0.03~0.1%, niobium 0.05~
A highly corrosion-resistant zirconium-based alloy characterized by comprising 5.0% of vanadium and one or more of 0.05 to 5.0 parts of vanadium, the balance being zirconium.